ScarfMence
I don't like Scarf Jirachi at all in a HO team, since after he revenge kills something, he becomes set-up bait for half the metagame with his mediocre power and awful STAB move (yeah Steel sucks as an offensive type if you didn't know). What is the point of revenge killing a fast threat if after doing so, we are going to get swept by another one?
Our Jirachi revenge killed an opposing AcroBat Gliscor with Ice Punch? Great, now we are going to get set-up on and swept by SD Terrakion, DD Gyara, Shell Smash Cloyster, QD Volcarona, and SD Lucario.
Our Jirachi revenge killed an opposing SD Scizor that was ready to sweep our team, with Fire Punch? Great, now we are going to get set-up on and swept by any DD dragon, QD Volcarona, Shell Smash Cloyster, DD Gyara, AcroBat Gliscor, SD Terrakion and more.
Anyway you get the point... Jirachi is so weak and gives so many set-up opportunities to the opponent after he revenge kills something, for a HO offensive team to afford. My opinion is that ScarfRachi's place is in balanced teams, which can handle the threats that can set-up on Jirachi with their defensive core.
In the other hand ScarMence is excellent in HO teams, as it can easily give us a winning condition when Steel types are weakened (not hard at all, considering we are using Haxorus and Zoroark), and can revenge kill the threats we need it to, without becoming set-up bait for half the set-up sweepers in the tier. As for the problem of who will tank Dragon hits, and any possible Scizor weakness, i think that Gyara and Donphan are enough to keep Scizor in check. Furthermore, we could easily put a Balloon Heatran in the last slot, to cover any possible Dragon weakness, give it SR so that Donphan will be free to use Ice Shard, and handle Scizor at the same time. Or we could even use a Passcho Berry lure Heatran, to lure and kill Starmie and Rotom-W which otherwise destroy the team...